An example of a conventional failure recovery scheme in a communication network is disclosed in Non-Patent Document 1 and Patent Document 1. This conventional failure recovery scheme in the communication network includes 1+1 protection (1+1 Unidirectional/Bidirectional Protection), 1:1 Protection, reservation type restoration (Shared Mesh Restoration), and path re-routing (LSP Re-routing), as disclosed in Non-Patent Document 1.
All of these failure recovery methods except for the path re-routing include previously determining preliminary routes for a currently-used route. For this reason, detouring the failure fails when multiple failures occur simultaneously on the currently used route and the preliminary route. As a result, in cases of multiple failures, the path re-routing as disclosed in Patent Document 1 has been applied.
Patent Document 1 discloses that when protection fails, path re-routing is performed under control of a GMPLS control unit. In such related art, a communication device includes a routing protocol unit, a topology DB for recording failures or empty bands of links reported by the routing protocol unit, and a signaling protocol unit for controlling paths.
Patent Document 1 also discloses the topology DB as a forwarding DB and the signaling protocol as a GMPLS control unit. Conventional path re-routing when the communication device having the above-described configuration is used is performed as follows.
After receiving a failure notification, the communication device deletes a currently-used path. The communication device then refers to the topology DB collected by the routing protocol to calculate a detour path that does not include failure locations. The communication device sets a new path along the detour route using a signaling protocol to recover from the communication failure.
However, such path re-routing has the following problems.
The first problem is that since it takes time for the routing protocol to notify the communication device of the failure location after the failure occurs, it is necessary to wait for a predetermined period of time in order to calculate the detour route and it takes time to recover from the failure.
Further, since it is impossible to detect whether the routing protocol was converged, it is not known whether a failure has occurred on the detour route calculated by referring to the topology DB of a start-point communication device. Therefore, when multiple failures occur, there is a possibility that a route including a failure location that is not present on the currently-used path is calculated, thus decreasing reliability of the calculated route.
The second problem is that, because a re-routing operation is dispersively performed, network resource contention may occur at intermediate communication nodes when a plurality of currently-used paths simultaneously fail. For example, referring to the network shown in FIG. 14, a link between communication devices B and C and a link between communication devices B and F have simultaneously failed. A communication device 1000 is disposed at a location encircled with a symbol A in FIG. 14. Similarly, communication devices 1000 are also disposed at locations encircled with symbols B, C, D, E, F, and G.
In FIG. 14, a transmission link between the communication device A and the communication device C is indicated by a transmission link 90-AC.
Here, a detour route for a currently-used path 1100 is calculated by the communication device A and a detour route for a currently-used path 1200 is calculated by the communication device D. In the detour route calculation, the communication device A or D does not consider the detour route of the communication device D or A. Accordingly, even when a link between the communication devices D and E or a link between the communication device E and B is an insufficient-band link having a band for only one detour path, a contention route is calculated through a shortest route calculation. Accordingly, one of the communication devices fails to set the detour path. In FIG. 14, the communication device A sets a detour route 1101 and the communication device D sets a detour route 1201. Accordingly, for example, a link between the communication device B and the communication device E becomes a contention link.
The third problem is that the currently-used path cannot be reverted to the original route after recovery from the failure. This is because the currently-used path needs to be deleted to set the detour route in order to reuse network resources other than those in a failure section that is being used by a failed currently-used path.
In general, the currently-used path is set as an optimal path in a range allowing the network to normally operate. For this reason, failure to revert to an original route of the currently-used path after recovery from all failures means that the optimal working state cannot be restored.
Non-Patent Document 1: J. Lang, Y. Rekhter, D. Papadimitriou, “RSVP-TE Extensions in Support of End-to-End Generalized Multi-Protocol Label Switching (GMPLS) Recovery,” IETF RFC4872. Chapters 5 to 11.
Patent Document 1: Japanese Patent Application No. 2002-125711 (Japanese Unexamined Patent Publication, First Publication No. 2003-318983)